All passenger vehicles manufactured in 1980 and later have some sort of computerised engine management system. Computerised engine management systems depend on a series of sensors that provide the information used to operate the engine at optimal efficiency. Current (as of February 2010) vehicle engine management systems primarily use Distributorless Ignition Systems (DIS), which eliminate many mechanical components and increase reliability and fuel efficiency.
Crankshaft Position Sensor
This sensor is also known as the Engine Speed Sensor (ESS). It provides data that enables the computer to know which cylinder should be fired at the crankshaft's present position. This sensor is essential to ensuring that the engine cylinders are always fired in the correct order. The Crankshaft Position Sensor (CPK) is always located somewhere on the engine in close proximity to the crankshaft, usually near the harmonic balancer or in the engine block aligned with a toothed wheel connected to the crankshaft. The CPK provides the data that is used to compute the engine's revolutions per minute (RPM), which is essential for proper transmission gear selection in relationship to vehicle speed and load.
There are three primary engine malfunction symptoms that may be indicators of CPK malfunction. If the vehicle engine is experiencing cylinder misfires, the CPK may not be providing the computer with accurate information on piston position. If the vehicle hesitates during acceleration, the CPK may not be providing cylinder position data to the computer fast enough to fire the appropriate cylinder to accelerate the vehicle in response to driver input. The most serious indication of CPK malfunction is intermittent start, and eventually no start. When the sensor fails, the computer will register a malfunction code and illuminate the check engine light on the instrument panel. There may be an indication of sensor failure due to defective electrical connections such as high resistance, or an open condition in the circuit going to the sensor or returning to the vehicle engine control module.
There are a number of internal engine problems that can cause the same symptoms as a defective CPK will. The most common problems that can be misdiagnosed as a faulty CPK are mechanical problems in the valve and timing mechanism, a faulty spark plug or a defective DIS module. Inaccurate interpretation of diagnostic codes can cause the mechanic to waste many hours looking for a problem that does not exist in the CPK. Internal engine mechanical malfunctions can cause cylinder misfires, hesitation and no-start conditions. Since significant engine disassembly may be required on some vehicles to reach the CPK, a mechanic would be well advised to insure that the symptoms being observed are really caused by this sensor.